Almost 80% of crop pollination by wild bees is provided by just 2% of the most common species, say scientists.

There are thousands of bee species in the world

In the UK, a small number of bees are
vital for crops such as oilseed rape, apples and strawberries, according
to the University of Reading team.

But protecting a wide range of bees
would "provide an insurance policy against future ecological shocks,
such as climate change", the scientists say.

The value of wild bee pollination is estimated at £1bn a year in the UK.

Prof Simon Potts, director of the Centre
for Agri-Environmental Research at Reading, said: "The few bee species
that currently pollinate our crops are unlikely to be the same types we
will need in the future.

"It is critical to protect a wide range
of bees and other insects now so that, as Britain's climate, environment
and crop varieties change, we can call on the pollinating species which
are best suited to the task.

"We can't just rely on our current starting line-up of pollinators.

"We need a large and diverse group of
species on the substitutes' bench, ready to join the game as soon as
they are needed, if we are to ensure food production remains stable."

Economic arguments

An international team of scientists reviewed data from five continents on the work of wild bees in pollinating crops.

The study, published in the journal
Nature Communications, indicated the pollinating work of wild bees was
worth about £1,900 per hectare globally.

Most of this work was done by a small number of common species, such as some types of bumblebees and solitary bees.

However, the researchers say
conservation efforts should be aimed at a wide number of species - even
those that currently contribute little to crop pollination - in order to
maintain biodiversity and ensure future food security.

Dr Mike Garratt, of the University of
Reading, said focusing only on wild bees that had financial value today
for agriculture would be a mistake.

"That misses the vast majority of bee
species," he said. "They are important pollinators of thousands of wild
plants - we can't afford to lose that either."

The research adds to debate over the value of economic factors in conservation.

Benefits that people gain from nature -
known as ecosystem services - are increasingly being used as an argument
for conservation efforts.

In the case of bees, too much focus on
services delivered - such as pollination - may lead to neglect of rarer
species that could be important in the future, the scientists say.

Commenting on the study, Prof Pat
Willmer of the University of St Andrews said: "The key point is that
wild bees, mostly the solitary bees, matter greatly for crop
pollination, just as many other studies just looking at one crop at a
time have already shown.

"But crucially the commonest wild bees
are the most important, which gives us the 'win-win' situation where
relatively cheap and easy conservation measures can support these and
give maximum benefit for the crops.

"For example, planting wild flowers with
wider grassy margins around crops, as well as less intensive or more
organic farming, all enhance abundance of the key crop-visiting bees."